Metals are commonly cast as ingots by pouring molten metal into one end opening of an open ended mold while the resulting body of partially solidified metal or ingot is advanced from the opposing end of the mold on a stool or support which is reciprocated in relation to the mold. To cast successfully, however, the operator must closely control the temperature of the metal, and this is accomplished by cooling the mold itself, and directing liquid coolant against the surface of the metal ingot as it emerges from the mold. The rate at which heat is extracted from the metal by the latter operation is a function of the temperature of the coolant itself, and the velocity of the coolant flow. For any given piece of molding equipment, the velocity is largely a function of the rate at which the coolant is discharged onto the ingot.
The ingot cooling rate at the start of the ingot drop is significantly higher than that when the ingot has reached thermal steady-state. At the start of the drop, both the support and the ingot cooling water chill the ingot butt. The rapid chilling of the ingot butt generates excessive thermal stress, which results in ingot butt deformation, such as butt curl. The severity of the ingot butt deformation is particularly apparent in ingots with a high width to thickness ratio, such as ingots having a width of approximately 1016–1829 mm (40–72 in.) and a thickness of approximately 508–660 mm (20–26 in.).
Butt curl is a problem primarily because it causes a portion of the ingot butt to lose contact with the bottom block at the start of the ingot drop. If this occurs for too long a time, molten metal in the ingot head crater may melt through the rising bottom and result in metal breakout or cracking. Likewise, if the curl rises faster than the lowering rate of the ingot, the molten metal may spill through the gap between the ingot and the mold, causing a yo-out. In addition, butt curl is an impediment to implementation of a start low-run low DC ingot casting practice, which can achieve improved ingot surface and increased casting rate.
It is known to one of ordinary skill in the casting art that ingot butt curl can be reduced by decreasing the ingot surface cooling during startup through low mold liquid application (e.g. less than about 0.4 gpm per inch mold perimeter). To minimize the coolant heat transfer rate on the ingot surface, mold liquid has to be run at an even lower flow rate (e.g. about 0.04 gpm per inch mold perimeter).
In a commercial single jet mold such a turn down of liquid flow is very difficult to implement. The liquid impingement location on the ingot surface of a commercial single jet mold would drift downward or fail to contact the ingot surface all together as the mold liquid flow rate is lowered. This would inhibit ingot cooling and cause it to bleed out. There are dual liquid coolant jet molds in the market place that would allow one of the jets to operate a low liquid mold. However, the degree of low water is still somewhat limited.
It is therefore a primary object of the present invention to provide a commercial single jet mold design for casting of metal ingots that has a lower minimum operation liquid flow rate while maintaining a constant liquid impingement location on the ingot surface, therefore creating superior ingot startup buff curl control and a lower than normal coolant heat transfer rate on the ingot surface.
Another object of the instant invention is to provide a commercial single jet mold design for the casting of metal ingots that substantially reduces the occurrence of ingot cracking due to inadequate ingot startup butt curl control and an abrupt change in the coolant heat transfer rate when cooling liquid is ramped from startup to steady state.
A further object of this invention is to provide a method for casting metal ingots with improved surface quality without the need for having multiple liquid coolant jets.
These and other objects and advantages are met or exceeded by the instant invention, and will become more fully understood and appreciated with reference to the following description.